1. Field
This invention is in the field of bending tools for tubing such as electrical metal tubing or plumbing tubing.
2. State of the Art
The installation of tubing such as electrical metal tubing encasing electrical wiring or copper plumbing tubing often requires that the tubing be bent to accommodate and circumvent physical barriers. Such bending is accomplished at the construction or installation site, and so requires a portable tube bending tool which will accurately bend such tubing into the desired arc. There are numerous styles and designs of tube bending tools, some of which require the operator's visual inspection of indicia on the bending tool in order to achieve an accurate bend, and others which have a stopping device which prevents the tubing from being bent beyond a pre-set angle. Each of these types of bending tools are limited in their usefulness.
Tools which require visual inspection of indicia on the tool are illustrated in Mount, U.S. Pat. No. 4,052,881; Kozinski, U.S. Pat. No. 4,269,056; Benfield, U.S. Pat. No. 3,718,018; Linquist, U.S. Pat. No. 4,009,602; and Vecho, Jr., U.S. Pat. No. 4,063,444 which show indicia on the tool itself which must be aligned with the bent tubing to measure the degree of bend accomplished, and D'Gerolamo, U.S. Pat. No. 4,425,784 which shows an air bubble gauge, similar to the one in a carpenter's level, mounted on the handle of the tool, which measures the angle of the bend. These tools are limited in their usefulness by the required visual inspection of either the indicia on the tool relative to the bend or the air bubble relative to the lines of the bubble gauge. Necessarily, use of tools requiring visual inspection is limited to well-lit installation or contruction sites. Furthermore, even in well-lit sites, it may be time consuming to visually inspect, and perhaps reinspect, the bending tool's indicia to determine the accuracy of the bend. Additionally, since operators may differ in their perception of when the tool's indicator lines are even with respect to the bent tubing, there may be a large degree of variation between one operator's work and another's.
Tools which rely on a stopping device that physically prevents bending beyond a predetermined point generally use a stopping device that is located on the bending anvil of the tool. A small error in adjusting the position of the device results in a magnified error in tube bending accuracy. This requires that the operator make extremely careful adjustments in order that an accurate bend be achieved due to the location of the stopping device itself. Because the adjustments must be carefully made, they are expensive with respect to operator's time. A stopping device for a tube bending tool is shown in Nason, U.S. Pat. No. 4,321,820. It features an adjustable gauge arm which extends from the handle of the bending tool, and which prevents bending beyond a predetermined arc. Such a tool requires that the portion of the tubing being bent be coplanar with the gauge arm. Depending on the shape of the obstruction around which the tubing must eventually fit, it may be necessary to bend the tubing into a variety of planes, and such a tool would not always provide an accurate means of arc measurements in these circumstances.
Innacurately bent tubing results in the loss of an operator's time and materials, losses which the operator seeks to minimize. Therefore, it is clear that there is a need for a tube bending tool which will provide accurate and consistent bending both in areas where visual inspection is limited and in situations where physical stopping devices are impractical.